Background: Antimicrobial peptides are on the first line of defense against pathogenic
microorganisms of many living beings. These compounds are considered natural antibiotics that
can overcome bacterial resistance to conventional antibiotics. Due to this characteristic, new peptides
with improved properties are quite appealing for designing new strategies for fighting pathogenic
Methods: Sixteen designed peptides were synthesized using Fmoc chemistry; five of them are
new cationic antimicrobial peptides (CAMPs) designed using a genetic algorithm that optimizes
the antibacterial activity based on selected physicochemical descriptors and 11 analog peptides derived
from these five peptides were designed and constructed by single amino acid substitutions.
These 16 peptides were structurally characterized and their biological activity was determined
against Escherichia coli O157:H7 (E. coli O157:H7), and methicillin-resistant strains of Staphylococcus
aureus (MRSA) and Pseudomonas aeruginosa (P. aeruginosa) were determined.
Results: These 16 peptides were folded into an α-helix structure in membrane-mimicking environment.
Among these 16 peptides, GIBIM-P5S9K (ATKKCGLFKILKGVGKI) showed the
highest antimicrobial activity against E. coli O157:H7 (MIC=10µM), methicillin-resistant Staphylococcus
aureus (MRSA) (MIC=25µM) and Pseudomonas aeruginosa (MIC=10 µM). Peptide
GIBIM-P5S9K caused permeabilization of the bacterial membrane at 25 µM as determined by the
Sytox Green uptake assay and the labelling of these bacteria by using the fluoresceinated peptide.
GIBIM-P5S9K seems to be specific for these bacteria because at 50 µM, it provoked lower than
40% of erythrocyte hemolysis.
Conclusion: New CAMPs have been designed using a genetic algorithm based on selected physicochemical
descriptors and single amino acid substitution. These CAMPs interacted quite specifically
with the bacterial cell membrane, GIBIM-P5S9K exhibiting high antibacterial activity on
Escherichia coli O157:H7, methicillin-resistant strains of Staphylococcus aureus and P.